Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor, which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels. The particulate matter sensor may be located upstream and/or downstream of a diesel particulate filler, and may be used to sense particulate matter loading on the particulate filter and diagnose operation of the particulate filter.
One example of a PM sensor is shown by Maeda et. al. in US 20120085146 A1. Therein, the particulate matter sensor is attached to the top of an exhaust pipe and housed within a cylindrical protection tube. The PM sensor additionally includes a sensor element that is positioned closer to a center of the exhaust pipe so that the sensor output more reasonably represents an average soot concentration in the exhaust pipe. In addition, the PM sensor includes inlet apertures configured to direct the exhaust into the sensor and towards the sensor element. Herein, the sensor element is positioned closer to the inlet holes to allow the sensor element to capture more of the incoming particulates.
However, the inventors have recognized potential issues with such sensor configurations. As one example, such an arrangement may make the sensor element more vulnerable to being contaminated by water droplets in the exhaust condensing at or near the inlet apertures. In such sensor configurations, additional protective coating may be required to protect the soot sensor element from direct impingement of larger particulates and water droplets. Adding additional protective layer may reduce the electrostatic attraction between the charged soot particles and the electrodes of the sensor element and may lead to reduced soot sensor sensitivity. With reduced sensitivity, the soot sensor may not be able to determine the leakage of the particulate filter in a reliable way. Thus, errors in the sensor may lead to a false indication of DPF degradation and unwarranted replacement of functioning filters.
On the other hand, if the sensor is mounted at the bottom of the exhaust pipe, as shown by Paterson in U.S. Pat. No. 8,310,249 B2, water condensing at the bottom of the exhaust pipe may overflow into the sensor element thereby contaminating the sensor element. Such contamination of the sensor element may lead to fluctuations in the output of the sensor, thereby decreasing the accuracy of estimating particulate loading on the particulate filter.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a particulate matter sensor for sensing particulate matter in an exhaust passage of an engine is provided. The particulate matter sensor comprises a spherical assembly, a support rod coupled to a bottom end of the spherical assembly, a plurality of flow tubes coupled to a top end of the spherical assembly, and a sensor element positioned within the spherical assembly, distal to the plurality of flow tubes. In this way, by separating the plurality of flow tubes from the sensor element, issues related to water droplets and larger contaminants impinging on the sensor element and causing fluctuations in the sensor output may be reduced.
As one example, an exhaust particulate matter sensor assembly may be positioned downstream of an exhaust particulate filter in an exhaust pipe. The particulate matter sensor may include a spherical assembly including a plurality of flow tubes attached to a top end of the assembly, and a sensor element positioned closer to a bottom end of the assembly. Specifically, the spherical assembly may include hollow spherical concentric outer and inner devices separated by a gap. A hollow support rod may be installed at the bottom end of the assembly coupling the assembly to a bottom of the exhaust pipe. By mounting the assembly on the support rod, the sensor element may be positioned closer to a center of the exhaust pipe.
The plurality of flow tubes coupled to the top of the assembly may include hollow cylindrical inner and outer tubes. As such, the outer tube may be an inlet tube mounted on top of the outer device and the inner tube may be an exit tube mounted on top of the inner device and positioned within the outer tube. In addition, the outer tube may include a plurality of perforations along the curved surface configured to direct the exhaust into the gap between the outer and the inner devices. Subsequently, the exhaust may be split into two portions; a larger portion of the exhaust inside the gap may be directed towards the sensor element positioned within the inner device via a hole located at the bottom of the inner device, and a smaller portion may be gravitated towards the bottom of the outer device. Herein, the smaller portion may include particulates having a larger than threshold size and hence may gravitate towards the bottom of the outer device. However, hollow rod is fluidically coupled to the outer device. Hence, the heavier particulates in the smaller portion of the exhaust may flow into the hollow rod, and further be drained out of the assembly. However, lighter soot particles in the larger portion of the exhaust may enter the inner device and may accumulate at the sensor element. As such, the sensor element may in turn be used to diagnose the functioning of the particulate filter. Herein, the sensor element is positioned away from the inlet tube and thus, by distancing the sensor element from the inlet tube, and further providing an alternative path for the heavier particulates, the sensor element may be protected and the sensor reliability may be increased.
In this way, the functioning of the sensor element may be improved and the sensor may be rendered more reliable. In addition, by enabling a more accurate diagnosis of the exhaust particulate filter, exhaust emissions compliance may be improved. This reduces the high warranty costs of replacing functional particulate filters. The exhaust may exit the sensor via the outlet tubes positioned on top of the assembly. The symmetrical design of the inlet and the outlet tube eliminate manufacture process for specific sensor orientation at the installation and enhance the sensor repeatability.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.